How are rainbows made?

Simple Science

At a glance

Sunlight is a mix of

different coloured

light

Light can only travel in

straight lines

When sunlight travels

through a raindrop it

is bent

Different colours are

bent by different

amounts and so the

raindrop splits the

sunlight into different

colours

Raindrops are near

perfect spheres and

so disperse the light

into a semi-circular

shape

Rainbows are one of natures most beautiful phenomena.

We know from experience that they appear during rain

showers in the presence of bright sunlight. They are

produced because of three properties of sunlight:

1. Sunlight is a combination of different coloured light

2. Light moves in straight lines

3. When light moves between one substance to another,

it bends

Water droplets fall from clouds as spheres. When its

raining, sunlight travelling through the atmosphere has to

travel through these drops to reach the ground. As the

sunlight enters into the raindrop it bends slightly. The

amount that the light bends depends on the colour of the

light, with blue light bending more than red light. This

causes the sunlight to spread out into its constituent colours

and is known as dispersion. As the sunlight travels through

the rain drop it reflects off the side of the raindrop.

Eventually the different colours of light exit the rain drop.

These colours reach our eyes causing us to see a rainbow.

Nicholas T 1

Alex Brown, 2012 7 Centre for Lifelong Learning